荷载/环境下钢管混凝土加固桥墩时变可靠度研究

The use of concrete filled steel tube retrofit damage piers can achieve good mechanical properties and economic benefits, and avoid environmental pollution and resource waste caused by reconstruction. It is in accordance with "four saving and one green" development strategy. However, the research on the long-term mechanical properties and time-varying reliability of concrete-filled steel tubular columns under load / environment is still insufficient to hinder its popularization and application. Therefore, the corrosion of retrofitted piers under the combine effects of load and environment, the tensile test of corroded steel tube and compressive test of corroded retrofitted piers were first conducted. The long-term mechanical mechanism of the retrofitted pier is studied from the material and structure level, thereby analyzing the influence of various parameters on the mechanical properties of reinforced column, and establishing a formula for calculating the bearing capacity based on limit equilibrium theory and finite element calculation. And then, the time-dependent functions of the retrofitted column resistance, the statistical analysis of the influence parameters, the combination of the load effect and the function of the limit state will be carried out. Finally, the reliability index of the retrofitted piers in various stages will be calculated by the Monte Carlo method and the decay law of the reliability with time will be obtained. The time-dependent reliability of the retrofitted piers during the predetermined life is required to not less than the target reliability to guide the reinforcement design and improve the reinforcement method.

利用钢管混凝土结构对损伤桥墩进行加固，可取得良好的力学性能和经济效益，同时避免拆除重建造成的环境污染和资源浪费，是符合“四节一环保”发展战略的研究课题。但目前研究集中于加固柱的短期力学性能，对其长期力学性能和时变可靠度研究尚有不足，严重阻碍该方法的推广应用。因此，本项目围绕这一关键问题，进行荷载/环境侵蚀下加固柱锈蚀试验、锈蚀钢管材性试验和锈蚀加固柱压力试验，分别从材料和结构层面揭示加固柱长期力学机理，分析各参数对加固柱力学性能的影响规律，并结合极限平衡理论和有限元计算结果建立承载力公式；开展加固柱抗力时变函数研究、影响参数的统计分析、荷载效应组合和极限状态功能函数研究后，将加固墩柱预期服役寿命分为有限个时不变阶段，利用蒙特卡洛法计算加固柱各阶段的可靠度指标，得出加固柱可靠度随时间的衰变规律，并通过预定寿命期内加固柱的时变可靠度不小于最低目标可靠度要求，保障结构长期安全，完善加固设计方法。

利用钢管混凝土结构优良的力学性能对受损桥墩进行加固，能够大幅度提高原柱结构承载力、延性和抗震性能。但目前研究集中于加固柱的短期力学性能，对其长期力学性能和时变可靠度研究尚有不足。因此，本项目开展荷载/环境侵蚀下加固柱的锈蚀试验，分别从材料和结构层面研究锈蚀对钢管和钢管混凝土加固柱力学性能影响规律。通过大量的锈蚀钢管标准拉伸试件试验结果，建立了锈蚀对钢管力学性能（包括弹性模量、屈服强度、极限强度和伸长率）的影响规律，并验算出锈蚀钢管屈服强度服从正太分布，得到了锈蚀钢管屈服强度平均值和标准差。由于目前对锈蚀钢管统计参数的选择多参考锈蚀钢筋和钢板，但钢管具有内表面锈蚀少而外表面锈蚀多的特征，其统计参数与钢筋和钢板又有所不同。因此，本研究弥补了锈蚀钢管统计参数的不足问题。在此基础上，通过锈蚀钢管混凝土柱受压力学性能试验，得到锈蚀后加固柱破坏形态、荷载-位移曲线和应力-应变曲线等，揭示加固柱刚度、承载能力和延性等性能的退化规律。并结合锈蚀钢管的材性试验，得到锈蚀钢管对核心混凝土套箍约束作用的变化规律，进而在未锈蚀加固柱抗力计算公式基础上，建立了锈蚀加固柱抗力随锈蚀增加的变化函数，揭示了加固柱的长期力学性能时变机理。计算50年的设计寿命内加固柱可靠度随时间的退化规律。根据加固柱寿命期内可靠度不低于规范允许的最低可靠度指标要求，反向指导加固柱截面和材料设计，形成基于时变可靠度的加固柱设计方法。